AC/DC inverter

ABSTRACT

An AC/DC inverter provided for transforming a DC power source into an AC power source, wherein the AC signal is used for driving a fluorescent filament. The inverter comprises a half-bridge switch electrically connected to the DC power source, wherein the half-bridge switch outputs the AC signal, a resonance groove circuit electrically connected to the half-bridge switch and the fluorescent filament, wherein the resonance groove circuit is provided for stepping up and filtering the AC signal into a high-voltage AC power source, providing a power for a load, and a controller feeding back an output of the fluorescent filament, providing a wavelength adjusting signal for controlling the conduction and cutting off of the half-bridge switch, such that the fluorescent filament can operate consistently and provide a consistent brightness.

BACKGROUND OF THE PRESENT INVENTION

1. Field of Invention

The present invention relates to an AC/DC inverter, and moreparticularly to an AC/DC inverter for driving a background fluorescentlight of an LCD, especially for a plurality of power operatedsemi-bridge AC/DC inverter designed for driving a plurality offluorescent light.

2. Description of Related Arts

As liquid crystal displays (LCD) thinner than conventional cathode raytube (CRT) monitors, they are being used in more and more homes andpublic display. However, since LCD is operated by its optical rotarypower and optical characteristic to display image and text information,hence not illuminable, it requires an additional background lightsource. An example of background light source for LCD is fluorescentfilament.

A typical AC/DC inverter utilizes a full-bridge inverter circuit, alongwith filtered waves from resonance grooves and a step-up transformer, aDC power input can be converted to a high AC voltage, so as to drive thefluorescent filament.

In order to stabilize the light emitted by the fluorescent filament, andprevent a change in light intensity while there is a change in the powerinput voltage, most inverters are incorporated with negative feedbackcircuits for stabilizing the electrical current of the fluorescentfilament. As the life-span of the fluorescent filament is affected bythe symmetry of the waveform of the electrical current, it is mostpopular to use full-bridge inverter to drive fluorescent filament.

Referring to FIG. 1 of the drawing, a conventional full-bridge inverteris illustrated. As shown in FIG. 1, a full-bridge inverter 100 comprisesa DC power source 101, a full-bridge switch 102, a resonance groove 103,a fluorescent filament 104, a current monitoring circuit 105, awavelength adjuster 106, a frequency producer 107 and a switch drivercircuit 108, wherein the full-bridge switch 102 comprises four powerswitches 101A, 101B, 101C and 101D. The resonance groove 103 comprises astep-up transformer 120 and two resonance capacitors 121 and 122. Thefrequency producer 107 comprises a triangular wave producer 110 and apulse producer 109. The switch driver circuit 108 provides four sets ofdriver output signal R1, R2, R3 and R4.

The DC power source 101 is electrically connected to the full-bridgeswitch 102, wherein the full-bridge switch output of the full-bridgeswitch 102 is electrically connected to a groove input of the resonancegroove 103. A groove output of the resonance groove 103 is electricallyconnected to a filament end of the fluorescent filament 104. Theconnection between the fill-bridge switch 102, the resonance groove 103and the fluorescent filament 104 is an example of a power transferconnection.

The current monitoring circuit 105 is electrically connected to thefluorescent filament 104 and the wavelength adjuster 106. The wavelengthadjuster 106 is then electrically connected to the frequency producer107 and the switch driver circuit 108, which is electrically connectedto the gate of the full-bridge switch 102, forming a control loopconnection.

Conventional full-bridge inverter is operated based on the a highfrequency conduction between the four power switches of the full-bridgeswitch 102, such that the DC voltage output by the DC power source 101is transformed to and outputted as a high-frequency AC square wave,which is provided for inputted to the resonance groove 103. Theresonance groove 103 utilizes the step-up characteristic and thewavelength filter function of the step-up transformer 120 to transformthe high-frequency AC square wave to a high frequency AC sine wave,which is provided to the fluorescent filament 104.

The control loop utilizes the current monitoring circuit 105 to producea feedback signal R5 which corresponds to a filament current, which isthen transferred to the wavelength adjuster 106. The wavelength adjuster106, together with the a triangular wave output R6 by the triangularwave producer 110 of the frequency producer 107, utilizing the theory ofnegative feedback, produces a wavelength adjusting signal R7 forinputting to the switch driver circuit 108, wherein the switch drivercircuit 108 utilizes the wavelength adjusting signal R7 and thefrequency producer 107 to produce the four sets of driver output signalR1, R2, R3 and R4 so as to drive the four power switches 101A, 101B,101C and 101D.

By controlling the conduction period between the two power switches 101A and 101D, and the conduction period between the two power switches101C and 101B, the alternating conduction between 101A and 101D, and101C and 101B provides the fluorescent filament a stable and AC currentthat has a symmetrical waveform.

This conventional type of full-bridge inverter circuits can stablycontrol the current of a fluorescent filament, however, has the drawback of having a great number of switches, pushing the production costof such circuits higher.

As a result, the present invention is to provide a cheaper and morereliable AC/DC inverter.

SUMMARY OF THE INVENTION

A main object of the present invention is to provide a circuitry of anAC/DC inverter for driving a fluorescent filament circuit, wherein theAC/DC inverter uses less power switches to control the operation of thefluorescent filament, producing lower DC voltage ripple, which in turnlowers noise caused by system ripples.

Another object of the present invention is to provide the circuitry of ahalf-bridge AC/DC inverter, having an advantage of using less powerswitches and lower production cost, together with an alternatingoperation to achieve lower DC voltage ripple, which in turn lowers noisecaused by system ripples when multi fluorescent filament is operated.

Another object of the present invention is to provide two series ofpower switch output signal of the AC/DC inverter, such that theoperation period of each of the series of power switch output signalalters symmetrically with respect to that of the other power switchoutput signal. Since the power switches do not conduct simultaneouslyupon receiving DC voltage, voltage noise of the power source isminimized.

Another object of the present invention is to provide a plurality ofseries of power switch output signal of the AC/DC inverter, which isapplied to a plurality of fluorescent filaments, such that thefluorescent filaments can utilize frequency producers with identicalfrequency aligned differently as frequency sources.

Accordingly, in order to accomplish the above objects, the presentinvention provides an AC/DC inverter for transforming a DC power sourceto an AC power source, the AC signal of which is used to drive afluorescent filament, wherein the AC/DC inverter comprises:

a half-bridge switch electrically connected to the DC power source;

a resonance groove circuit electrically connected to the DC power sourceand the fluorescent filament, wherein the resonance groove circuitsteps-up and filters the AC signal, such that the AC signal istransformed to an the AC power source; and

a controller feeding back a filament output of the fluorescent filament,providing a wavelength adjuster, a wavelength adjusting signalcontrolling the conduction of the half-bridge switch, such that thefluorescent filament, according to the conduction condition of thehalf-bridge switch, can be operated around the resonance frequency.

These and other objectives, features, and advantages of the presentinvention will become apparent from the following detailed description,the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art of a full-bridge fluorescent filamentinverter circuitry.

FIG. 2 illustrates a circuitry of an AC/DC inverter according to apreferred embodiment of the present invention.

FIG. 3 illustrates some wave form of the circuitry of the AC/DC inverteraccording to the above preferred embodiment of the present invention.

FIG. 4 illustrates a circuitry of two AC/DC inverters according to analternative embodiment of the present invention.

FIG. 5 illustrates a sequential marked graph according to the abovealternative embodiment of the present invention.

FIG. 6 illustrates a circuitry of a plurality of AC/DC invertersaccording to yet another alternative embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 2 of the drawings, a circuitry of an AC/DC inverteraccording to the preferred embodiment of the present invention isillustrated, wherein the AC/DC inverter is a half-bridge AC/DC inverter.

As shown in the drawing, an inverter controller 200 comprises a DC powersource 201, a half-bridge switch 202, a resonance groove 203, afluorescent filament 204, a current monitoring circuit 205, a voltagemonitoring circuit 206 of the filament terminal, a wavelength adjuster207, a frequency producer 208, a switch driver circuit 209, which is ahalf-bridge switch driver circuit, a protection circuit 210, a timer 211and a brightness adjusting circuit 212.

The DC power source 201 is electrically connected to the half-bridgeswitch 202, wherein, through a switch output of the half-bridge switch202, the half-bridge switch 202 is electrically connected to theresonance groove 203, though a resonance groove input of the resonancegroove 203. Through a resonance groove output, the resonance groove 203is also electrically connected to the fluorescent filament 204 through afilament end. The resonance groove 203 further comprises a step-uptransformer 221 and resonance capacitors 222, 223, and 224.

The electrical connection method between the elements of the AC/DCinverter is conventionally known as power transfer connection. Accordingto the preferred embodiment of the present invention, a Low Q resonancegroove is used, so as to provide easy designing of the circuitry.

Under such a circuitry design, the waves that drive the step-uptransformer 221, and the fluorescent filament 204 is quasi sine waves orquasi square waves, as oppose to pure square waves or pure sinusoidalwaves. FIG. 3 of the drawings illustrates the voltage wave form atdifferent positions under the power transfer route design according tothe preferred embodiment.

In FIG. 3 of the drawings, S51 is the voltage waveform of the switchoutput end of the half-bridge switch 202 and S16 is the filament drivingvoltage waveform output by the step-up transformer 221.

The current monitoring circuit 205 and the voltage monitoring circuit206 of the filament terminal are electrically connected to the ends ofthe fluorescent filament 204 respectively. The current monitoringcircuit 205 is also electrically connected to the wavelength adjuster207, wherein the wavelength adjuster 207 is also electrically connectedto the frequency producer 208 and the switch driver circuit 209. Theswitch driver circuit 209 is in turn electrically connected to thehalf-bridge switch 202, forming a control loop connection.

The half-bridge switch 202 comprises two power switches 202A and 202B.According to the preferred embodiment of the present invention, thepower switch 202A is a P-type MOSFET, while the power switch 202B is anN-type MOSFET. However, the power switches are not limited to MOSFET,and can also be crystal switches, such as BJT switches.

The frequency producer 208 produces a triangular wave signal SI and apulse signal S2, wherein both signals have the same frequency. However,the present invention is not limited to the use of triangular wavesignals, where all ramp signals and sawtooth wave signals areapplicable.

The current monitoring circuit 205 and the fluorescent filament 204 areelectrically connected to provide a signal S3 for instructing theconduction of the fluorescent filament 204, and utilize a second signalS4 to show the current value of the current flowing through thefluorescent filament 204. The voltage monitoring circuit 206 of thefilament terminal utilizes the resonance capacitors 223, and 224 of theresonance groove 203 to obtain a third signal S5 for instructing aterminal voltage of the fluorescent filament 204.

The wavelength adjuster 207 comprises an error amplifier 261, a reversedifferentiator comprises a resistor 262 and an adjuster capacitor 263,and a comparator 264. The wavelength adjuster 207 also comprises acontrolled power source 265, which is electrically connected to anamplifier inverse input of the error amplifier 261 through a switch 266.

The switch driver circuit 209 comprises two driver output signals POUTand NOUT. The protection circuit 210 comprises a logic control circuit272 receives the signal S3, the third signal S5 and an output signal S6of the error amplifier 261 in the wavelength adjuster 207.

The timer 211 comprises two timer comparators 281 and 282, and a timerpower source 283. The brightness adjusting circuit 212 comprises abrightness frequency producer 291, wherein a brightness triangularsignal S7 and a brightness control voltage S8 is produced by thebrightness frequency producer 291. The brightness triangular signal S7is transmitted to a non-inverse input of a brightness comparator 293,and the brightness control voltage S8 is transmitted to an inverse inputof the brightness comparator 293. After comparison, an adjusting pulsesignal S9 is produced, which comprises an OR gate 296 for controllingthe timing of the outputting of the adjusting pulse signal S9 to thewavelength adjuster 207.

According to the preferred embodiment of the present invention, thetimer 211 functions in a manner such that a timer capacitor 284 is beingcharged by the timer power source 283, such that a timer capacitorvoltage S12 of the timer capacitor 284 increases as time increases.Before the timer capacitor voltage S12 reaches a first reference voltageVref1, a reset signal S11 is being sent out. And when the timercapacitor voltage S12 reaches a second reference voltage Vref2, a timeout signal S10 will be sent out.

The timer power source 283 is being controlled by a power control signalS13, such that when the voltage of the system is lower than a thirdreference voltage Vref3, the power source 283 will be cut off, and thetimer capacitor voltage S12 of the timer capacitor 284 earthed. Throughsuch design, every time when the system starts up the DC power source201 from a zero voltage, the timer capacitor 284 of the timer 211 ischarged started from zero voltage.

According to the preferred embodiment of the present invention, thefrequency producer 208 is also controlled by a fourth signal S14,indicating whether or not the fluorescent filament is conducted. Whenthe fluorescent filament is conducted, an operation frequency is sentout. And when the fluorescent filament is not conducted, a start-upfrequency is sent out.

An advantage of such a design is that the resonance frequency of theresonance groove 203 can operate by the different filament frequencyaccording to the conduction condition of the fluorescent filament, suchthat the system can be operated around the resonance frequency, whetheror not the fluorescent filament is conducted, such that the system isoperated efficiently.

The fourth signal S14 is determined by the signal S3 provided by thecurrent monitoring circuit 205, and a protection circuit comparator 274of the protection circuit 210, such that when the signal S3 exceeds afourth reference voltage of Vref4, the fluorescent filament 204 isconsidered as being conducted.

Under normal circumstances, the detailed operation procedures accordingto the preferred embodiment of the present invention are as follows:

After staring up the electrical connection, the timer 211 initializesthe charging of the timer capacitor 284, such that before the timercapacitor voltage reaches the first reference voltage Vref1, the resetsignal S11 being sent out by the timer 211 passes through an OR gate267, turning on a switch 266, such that the power source 265 isconnected to the inverse input of the error magnifier 261, forcing aninverse input voltage of the input of the error magnifier 261 to behigher than a fifth reference voltage Vref5, which in turn forces anerror magnifier output to be zero.

When the timer capacitor 284 continue to charge until the capacitorvoltage is greater than the first reference voltage Vref1, the powerswitch 266 will be turned off, such that the wavelength adjuster 207 isinitialized, and because of the fluorescent filament 204 is notconducted, the non-inverse input voltage of the error magnifier 261becomes lower than the fifth reference voltage Vref5, causing the outputsignal S6 outputted by the error magnifier 261 to increase, under theeffect of negative feedback.

And, after comparing with the triangular wave signal S1, the comparator264 of the wavelength adjuster 207 outputs a wavelength adjusting signalS15. The switch driver circuit 209 receives the wavelength adjustingsignal S15 and the pulse signal S2 so as to produce the driver outputsignals POUT and NOUT to drive the power switch 202A and 202Brespectively.

Before the conduction of the fluorescent filament 204, the filamentdriving voltage S16 will increase due to a widening of an operationperiod of the wavelength adjusting signal S15. Upon sensing the thirdsignal S5 exceeding a sixth reference voltage Vref6, the voltagemonitoring circuit 206 sends out a voltage overloading signal S17, whichpasses through the OR gate 267 and turn on the switch 266 of the powersource 265, to the non-inverse input of the error magnifier 261, so asto reduce the output signal S6 of the error magnifier 261, wherebydecreasing the operation period of the wavelength adjusting signal S15and decreasing the amount of electrical power input to the fluorescentfilament.

If the effect of this decreasing in amount of electrical power input tothe fluorescent filament is a sensing of the third signal S5 to be lessthan the sixth reference voltage Vref6, the switch 266 will be turnedoff, increasing the output signal S6 of the error magnifier 261. As aresult, the filament driving voltage S16 is stably adjusted under such anegative feedback control.

As soon as the fluorescent filament is conducted by a sufficientfilament driving voltage S16 and for a substantial period of time,according to the characteristic of the fluorescent filament, thefilament driving voltage S16 will drop to less than half the voltagerequired for conducted operation, such that the voltage monitoringcircuit 206 of the filament terminal loses its function due to anon-detection of a higher voltage.

At the same time, the current monitoring circuit 205 sends out thesignal S3 to the protection circuit 210, producing the fourth signal S14 to alter the output frequency of the frequency producer 208, andoutputting the second signal S4 to the wavelength adjuster 207, suchthat the current flowing through the fluorescent filament is stabilizedon a pre-determined value through the negative feedback control.

According to the preferred embodiment of the present invention, theprotection circuit is operated as follows:

When the fluorescent filament is not connected, the third signal S5 willcontinuously send out a signal indicating that the terminal voltage ofthe fluorescent filament exceeds the sixth reference voltage Vref6 tothe logic control circuit 272, which receives the time out signal S10 ofthe timer 211.

The logic control circuit 272 will take no action until the time outsignal S10 is inputted. Once the time out signal S10 reaches the logiccontrol circuit 272, and in the condition of the filament terminalvoltage is exceeds the sixth reference voltage Vref6, it times with adigital timer, by the pulse signal S2 produced by the frequency producer208 to time.

If the filament terminal voltage still exceeds the sixth referencevoltage Vref6 after a predetermined period of time, a terminating signalS18 will be outputted by the logic control circuit 272 to the switchdriver circuit 209, so as to cut off the conduction between the powerswitches 202A and 202B.

If the fluorescent filament is damaged during operation, the fourthsignal S14 will be sent out, indicating that the fluorescent filament isnot conducted, to the logic control circuit 272, receiving the time outsignal S10 from the timer 211. The logic control circuit 272 will nottake any action until the receiving the time out signal S10.

When time is up, the logic control circuit 272, under the condition ofthe fourth signal S14 indicating that the fluorescent filament is notconducted, will time with a second digital timer, through a second pulsesignal S21 produced by the low frequency brightness adjusting circuit212.

If the filament still is not conducted after a predetermined period oftime, the logic control circuit 272 will output the terminating signalS18 to the switch driver circuit 209, so as to cut off the conductionbetween the power switches 202A and 202B.

Also, when, the step-up transformer 221 encounters serious damage, suchas power leakage, creating an overloading effect, the entire system willbe overloaded. Under such conditions, the error magnifier 261 willcontinue to increase its outputting of the output signal S6, so as toprovide sufficient power to stabilize the current of the fluorescentfilament. And if the leakage is greater than the maximum power providedby the system, the error magnifier 261 will definitely exceed the peakvalue of the triangular wave signal S1.

The protection circuit 210 compares the output signal S6 of the errormagnifier 261 with a seventh reference voltage Vref7, the value of whichis slightly higher than the peak value of the triangular wave signal, toobtain an overloading signal S19, indicating whether or not the systemis overloaded.

Similarly, if the overloading signal S19 indicates that the system isoverloaded when the timer 211 initializes the protection circuit 210,and, if the timing using the pulse signal S2, which passes through thelogic control circuit 272 and is produced by the frequency producer 208,also exceeds the predetermined period of time, the logic control circuit272 then outputs the terminating signal S18 to the switch driver circuit209, cutting off the conduction between the power switches 202A and202B.

According to the preferred embodiment of the present invention, theinverter further has the brightness adjusting circuit 212 provided forcontrolling the termination and restarting of the power provided to thefluorescent filament. It makes use of the adjusting of brightness ratioto adjust the brightness of the fluorescent filament. And, in order toavoid the creating of the flashing feeling created by a low frequency,the brightness frequency is normally controlled to be above 200 Hz.

The brightness adjusting circuit is controlled by two signals, the firstone being the fourth signal S14 indicating whether or not thefluorescent filament is conducted, and the second one being the time outsignal S10 of the timer 211. Only when the fourth signal S14 indicatesthat the fluorescent filament is conducted or the timer 211 receives thetime out signal S10 will a brightness control switch 236 controlling theoutput of the brightness adjusting signal be turned on.

A brightness adjusting voltage S20 of the brightness adjusting circuitis higher than the fifth reference voltage Vref5. When the brightnessadjusting voltage S20 passes through the brightness control switches 235and 236 to be connected to a second resistor 234 and the wavelengthadjuster 207, the output signal S6 of the error magnifier 261 of thewavelength adjuster 297 is decreased, cutting off electricitytransferring of the system to avoid overloading.

And when the brightness control switch 235 is turned off by theadjusting pulse signal S9, the wavelength adjuster 207 reopens thecircuit, restarting to provide electrical power to the system.

Brightness adjusting effect can be achieved by a low frequency tocontrol the ratio between the stopping and the restarting of providingelectrical power of each cycle. In order to ensure that the fluorescentfilament has sufficient and continuous electrical power so as to lightup in a predefined period of time, the time when brightness can beadjusted is determined by whether or not the fluorescent filament isconducted.

In order to provide an AC driven fluorescent filament 204 with goodsymmetry, according to the preferred embodiment of the presentinvention, when the system is operated steadily, the half-bridge switch202 is alternately conducted with the same conduction period, but offsetby 180 degrees.

Referring to FIG. 4 of the drawings, an alternative embodiment of thepresent invention is illustrated, wherein two sets of AC/DC invertersare operated and applied to two fluorescent filaments simultaneously.The elements in each of a first inverter set 301 and a second inverterset 302 is substantially the same as that of the AC/DC inverter as shownin FIG. 2 of the drawings.

It should be noted that a timer 303 is shared by the first and thesecond inverter set 301 and 302, and, in order to be applicable to thetwo sets of inverters according to this embodiment of the presentinvention, a frequency producer 304 and a brightness adjusting circuit305 must be appropriately altered.

A frequency control signal T3 of the frequency producer 304 determineswhen a change in frequency is required, according to a first conductionconfirmation signal T1 and a second conduction confirmation signal T2 ofthe first and the second inverter set 301 and 302 respectively, and atimer signal T4 of the timer 303.

After passing the conduction confirmation signals Ti and T2 through anAND gate 311, a third conduction confirmation signal T5 is obtained.And, after passing the third conduction confirmation signal T5 and thetimer signal T4 though an OR gate 312, the frequency control signal T3is obtained.

An operation frequency of the frequency producer 304 will be changedafter the fluorescent filaments are conducted and the timer signal T4outputted by the timer 303. As a result, the frequency of the system canstill be altered even when one of the fluorescent filaments is damaged.

The frequency control signal T3 is also used for controlling thebrightness adjusting circuit 305. The outputting moment of thebrightness adjusting circuit 305 for adjusting the brightness is alsoafter the conduction of the fluorescent filaments, or after the timer303 outputted the timer signal 304. As a result, not only can it beensured that both filaments are successfully lit up, brightnessadjustment can still be achieved even when one of the filaments isdamaged.

A second pulse signal T7 is produced when a first pulse signal T6, whichis outputted by the frequency producer 304 to the AC/DC inverter, passesthrough an inverter 313. Utilizing the first pulse signal T6 and thesecond pulse signal T7 having the same frequency as but out of phase ofthe first pulse signal T6, such that the first AC/DC inverter outputs afirst set of driver output signals POUT1 and NOUT1, for driving a firstpower switch P1 and N1.

The second AC/DC inverter outputs a second set of driver out signalsPOUT2 and NOUT2 for driving a second power switch P2 and N2, wherein thesecond set of driver output signals has the same frequency as but out ofphase of the first set of driver output signals.

Referring to FIG. 5 of the drawings, a sequential marked graph of thedriver output signals according to this alternative embodiment of thepresent invention is illustrated. The dashed portion of FIG. 5 shows thechange in operation periods of the driver output signals POUT1, NOUT1and POUT2, NOUT2.

In order to keep the symmetry of the filament driving current, thechange between the operation period between the driver output signalsPOUT1, NOUT1 and POUT2, NOUT2 is symmetrical. Since the driver outputsignals POUT1 and POUT2 will not be conducted simultaneously, a voltagenoise of the power source will be reduced.

Referring to FIG. 3 of the drawings, because POUT1 and POUT2 is out ofphase by 180 degrees, the current flowing into the fluorescent filament318 and 319 will be reversed. Also, by adjusting the polarity of thetransformers 321 and 322, POUT1 and POUT2 can be altered to be in phase.

When more than two fluorescent filament are in use, a plurality offrequency producer, each having the same frequency but out of phase witheach other, is used as a frequency source to drive the fluorescentfilament.

Referring to FIG. 6 of the drawings, a plurality of frequency producerprovided for driving N number of AC/DC inverters according to thisalternative embodiment of the present invention is illustrated. Theinput of the plurality of frequency producer 501 can be an externaltime-pulse 502, which can be a random frequency related to themonitoring control while the LCD display is being operated. The otherinput is a frequency control signal 503.

The frequency control signal 503 utilizes an AND gate 504 and an OR gate505 to control the operation frequency of the fluorescent filament,according to the conduction confirmation signals 506, 507, 508 . . . N,confirming whether or not all the N number of fluorescent filaments areconducted, or upon the outputting of a timer signal 509 by the timer.

Each of the triangular wave signal 510 output by the plurality offrequency producer 501 to each of the wavelength adjuster has the samefrequency but out of phase. Each of the pulse signal 511 output to eachof the switch driver circuit has the same frequency as and in phase withthe triangular wave signal 510.

After entering the frequency producer 501, another plurality ofbrightness control output 531 produces a brightness control signal 532that is produced when the monitor frequency is related, such that thefrequency control signal 503 controls the conduction switch 533, so asto control when the brightness control signal 532 is outputted to eachof the AC/DC inverter.

Such a plurality of frequency producer 501 can be achieved by the use ofa conventional micro control unit (MCU) 521, together with a directdigital synthesizer (DDS) 522.

Due to the fact that not the power switch of the DC power source willnot be conducted all at the same time, as oppose to conventionalcircuitry, noises related to the power source is minimized. And sincethe operation frequency is synchronized with the monitor, visualdisturbance due to interference caused by frequency difference.

The usage of the outputting method of the frequency producer is notlimited to half-bridge AC/DC inverters. When there are more than twosets of fluorescent filament, this outputting method can also be appliedfull-bridge or other same random frequency control system, so as tominimize noises related to the power source and visual disturbance.Also, the present invention utilizes fluorescent filament to illustratethe preferred embodiment, but its application should not be limited tofluorescent filament. The present invention as disclosed above can beapplied to any lighting element.

One skilled in the art will understand that the embodiment of thepresent invention as shown in the drawings and described above isexemplary only and not intended to be limiting.

It will thus be seen that the objects of the present invention have beenfully and effectively accomplished. It embodiments have been shown anddescribed for the purposes of illustrating the functional and structuralprinciples of the present invention and is subject to change withoutdeparture from such principles. Therefore, this invention includes allmodifications encompassed within the spirit and scope of the followingclaims.

1. An AC/DC inverter for inverting a DC power source to an AC powersource to drive a load, comprises: a half-bridge switch electricallyconnected to said DC power source, wherein an AC signal is invertedtherefrom by said half-bridge switch; a resonance groove circuit, ahaving resonance frequency, electrically connected to said half-bridgeswitch and said load, wherein said resonance groove circuit increases avoltage and filters a waveform said AC signal to form said AC powersource for said load; and a controller provided for feeding back anoutput of said load, providing a wavelength adjusting signal to controla conduction and a cutting off of said half-bridge switch allowing saidload to operate close to said resonance frequency.
 2. The AC/DCinverter, as recited in claim 1, wherein said load is a gaseousdischarge lamp.
 3. The AC/DC inverter, as recited in claim 1, whereinsaid gaseous discharge lamp is a fluorescent filament.
 4. The AC/DCinverter, as recited in claim 1, wherein said AC signal is a square wavesignal.
 5. The AC/DC inverter, as recited in claim 1, wherein said ACsignal is a quasi sine wave signal.
 6. The AC/DC inverter, as recited inclaim 1, wherein said AC signal is a quasi square wave signal.